1. Field of the Invention
The present invention relates to an optical pickup device, and more particularly to a compatible optical pickup device for recording/reproducing with respect to different kinds of optical discs.
2. Disclosure of Related Art
Currently, there exist various kinds of optical discs, such as Blu-ray Disc (BD), High-Definition Digital Versatile Disc (HDDVD), Digital Versatile Disc (DVD), and Compact Disc (CD). In view of this, there is a demand for a compatible optical pickup device compatible with these various kinds of optical discs.
There is known a compatible optical pickup device, wherein laser light emitted from one light source is distributed to two objective lenses so that the optical pickup device is compatible with both of BD and HDDVD. In this arrangement, the focus positions by the each of the objective lenses are different from each other in the disc thickness direction. Further, it is possible to configure an optical pickup device compatible with both of BD and CD by forming a diffraction hologram on an incident surface of an objective lens. In the above arrangement, however, if a hologram is formed in such a manner as to form one focal point with respect to BD, laser light for CD is focused at two positions i.e. forward and rearward positions in the optical axis direction, because of a wavelength difference between laser light for CD and laser light for BD.
As described above, if two focal points are formed with respect to one laser light, in the case where one of the two focal points is positioned on a recording layer, laser light to be converged on the other of the two focal points may be entered into a photodetector as stray light. The stray light may deteriorate a signal from the photodetector. In view of the above, in the compatible optical pickup device, it is necessary to provide an arrangement of suppressing incidence of stray light into a photodetector.